When an original acoustic signal is emitted in a reverberant medium then picked up by a microphone, the microphone picks up a reverberated signal that is dependent on the reverberant medium.
In the following, the term “anechoic acoustic signal” is understood to mean the original acoustic signal that is not reverberated by a medium. An anechoic acoustic signal can sometimes be directly recorded by a microphone, for example when the original acoustic signal is emitted in an anechoic chamber.
However, under common recording conditions, a microphone records a reverberated acoustic signal which is a signal consisting of the original acoustic signal received directly, but also reflections of the original acoustic signal on the reverberant elements of the medium, for example the walls of a room.
Strong acoustic reverberation of the medium can be particularly bothersome since it degrades the quality of the recorded sound and reduces speech intelligibility and speech recognition by machines.
To solve this problem, methods and devices are known for reconstructing the amplitude of a dereverberated signal from an acoustic signal reverberated by a medium.
In the present application, “dereverberated signal” means an estimate of the original acoustic signal, or anechoic signal, obtained by analog or digital processing of a reverberated acoustic signal recorded by a microphone.
By way of example, patent US201603667 describes a dereverberation method which reconstructs a dereverberated signal from an acoustic signal reverberated by a medium, by calculating the amplitude of the dereverberated signal in several frequency bands.
There is a need to further improve the performance of such methods by more accurately estimating the characteristics of the dereverberated signal from a reverberated acoustic signal recorded by a microphone.
Another method is described in the paper “Restoration of instantaneous amplitude and phase of speech signal in noisy reverberant environments” by Yang Liu et al., published in the reports of the 23rd European Signal Processing Conference. This paper describes a supervised method for teaching a Kalman filter to reconstruct the phase and amplitude of a dereverberated signal using a training database consisting of a pair of reverberant and anechoic signals. Such a database, however, is complicated to collect and the results obtained are highly dependent on the quality of the training database and on the fit between the types of reverberations present in the signals of the training database and the reverberations appearing in the actual applications. In addition, the Kalman filter dereverberation method described in that document only allows for linear amplitude and phase modulations, meaning those in which the temporal derivatives of the amplitude and of the phase, dereverberated, are constant over time.
The present invention improves this situation.